Fibrous structures containing nanofibrils and other textile fibers

ABSTRACT

Nanofibers are produced having a diameter ranging from about 4 Å to 1 nm, and a nano denier of about 10 −9 . The use of the electro-spinning process permits production of the desired nanofibrils. These fibrils in combination with a carrier or strengthening fibers/filaments can be converted directly into nonwoven fibrous assemblies or converted into linear assemblies(yarns) before weaving, braiding or knitting into 2-dimensional and 3-dimensional fabrics. The electrospun fiber can be fed in an air vortex spinning apparatus developed to form a linear fibrous assembly. The process makes use of an air stream in a properly confined cavity. The vortex of air provides a gentle means to convert a mixture of the fibril fed directly or indirectly from the ESP unit and a fiber mass or filament into an integral assembly with proper level of orientation. Incorporation of thus produced woven products into tissue engineering is part of the present invention.

This application is a division of Ser. No. 09/169,116 filed Oct. 8,1998, U.S. Pat. No. 6,106,913 which claims benefit of Provisional No.60/061,611 filed Oct. 10, 1997.

FIELD OF THE INVENTION

The present invention is directed towards an improved fibrous structure.More particularly, the present invention relates to lineartwo-dimensional and three-dimensional textile structures.

BACKGROUND OF THE INVENTION

Linear, 2-dimensional and 3-dimensional textile structures have foundnew uses beyond traditional apparel in recent years because of theirunique combination of light weight, flexibility, permeability, andstrength and toughness. Many of these applications including but notlimited to medical, chemical separation, chemical protection require abroad range of fiber architecture, packing density, surface texture,porosity, total reactive surface areas and fiber tortuosity.

Some early work on fiber structures are discussed in an article by FrankK. Ko entitled Three Dimensional Fabrics for Composites, in TextileStructural Composites, Chou, T. W., and Ko, F. K., eds., Elsevier, 1989.Another discussion of the prior art is by Frank K. Ko entitled PreformFiber Architecture for Ceramic Matrix Composites, Bull Am. Cer. Soc.February, 1989.

A key element dictating the range of these physical characteristics isthe fineness (diameter, linear density-denier) of the constituent fibersand the way these fibers are organized and oriented. For many years, therange of fiber fineness expressed in terms of fiber diameter are wellabove 2 μm.

It would be of great advantage in the art if fibers of smaller diametercould be prepared for these applications. Another advantage would be ifthose smaller fibers could be made stronger.

Accordingly, it is an object of the present invention to provide amethod of making fibers of much smaller diameter, in the range of whatare known as nanofibrils.

Another object of this invention is to provide nanofibrils with adequatestrength to permit their use in textile processing processes.

Other objects will appear hereinafter.

SUMMARY OF THE INVENTION

It has now been discovered that the above and other objects of thepresent invention may be accomplished in the following manner.Specifically, it has been discovered that it is now possible to producefibrils—fibers in the nanometer diameter level.

One current limitation of these fibrils is their lack of sufficientstrength to withstand the rigors of textile processing. The fineness ofthese fibrils also make them prone to stick to surfaces during process.The lack of strength can be remedied by combining the fibrils withstronger fibers or filaments. The problems caused by surface contactscan be minimized by a pneumatic(air) or fluid based processing of thefibrils. These fibrils in combination with the carrier or strengtheningfibers/filaments can be converted directly into nonwoven fibrousassemblies or converted into linear assemblies(yarns) before weaving,braiding or knitting into 2-dimensional and 3-dimensional fabrics. Theuse of the electro-spinning process permits production of the desirednanofibrils.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference is herebymade to the drawings, in which:

FIG. 1 is a schematic diagram of a hybrid yarn spinning system inaccordance with the present invention;

FIG. 2 is a schematic illustration of nanofiber fabrication in acircular or rectangular loom; and

FIG. 3 is a schematic illustration of various 3-dimensional shapes thathave been fabricated in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Textile fibers have a fiber diameter ranging from 1 μm to 10 μm, and adenier ranging from 10⁻³ to 10. The lower diameters and deniers aremostly electrospun fibers, with nothing below 100 nm (nanometer) infiber diameter or 10⁻⁵ denier having been developed. Nanofibers, inaccordance with the present invention, have a diameter ranging fromabout 4 Å to 1 nm, and a nano denier of about 10⁻⁹.

The present invention permits the production of 2-dimensional and3-dimensional products including nanofibers by the use of theelectrospinning process. This spinning process makes it possible toproduce fibrils—fibers in the nanometer diameter range. It has beendiscovered that the inherent lack of strength of these very fine fibrilscan be remedied by combining the fibrils with stronger fibers orfilaments. It has also been found that problems caused by surfacecontacts can be minimized by a pneumatic or fluidic processing of thefibrils. The fibrils of this invention can, in combination with thecarrier or strengthening fibers/filaments be converted directly intononwoven fibrous assemblies or converted into linear assemblies or yarnsbefore weaving, braiding or knitting into 2-dimensional and3-dimensional fabrics.

The Air Vortex Spinning (AVS) Process used to form nanofibers is shownin FIG. 1. The electrospun fiber can be fed in an air vortex spinningapparatus developed to form a linear fibrous assembly, as illustrated inFIG. 1. The process makes use of an air stream in a properly confinedcavity. The vortex of air provides a gentle means to convert a mixtureof the fibril fed directly or indirectly from the ESP unit and a fibermass or filament into an integral assembly with proper level oforientation.

Turning now to FIG. 1, the operation of the AVS, 10 generally, isdescribed in more detail In its simplified form the AVS uses theprinciple of an air vortex created helical current, which current isresponsible for the amount of twist and entanglement which is forwardedto the yarn. The air vortex helical current is created by a tangentialinflux of air pressure via inlet 11 from an electrostatic chamber 12 bya tangential influx of air pressure into the top of the spinning zone13, comprising a spinning tube 14, and also including an air suctionoutlet 15 at the bottom of the spinning tube 14. Thus a helical as wellas a vortex type velocity current is created inside zone 13. Twist andentanglement is imparted to the yarn by this mechanism. Control of theseinitial factors control the final structure of the yarn assembly.

At the point of introduction of fibers 17 via inlet 11, those fibers 17have been electrostatically charged by electrostatic current source 18,and are then whirled in a looped configuration in the helical-vortex aircurrent, at the open end or tail section of the yarn 19. By means of theaforementioned air current, fibers are simultaneously transferred,attached, twisted, and drawn off in the form of yarn 19. on to a take-uproll 21. Input tube 11 introduces fibers 17 at an acute angle tangentialto the axis of spinning zone 13, and may be supplied from varioussources such as containers of fibers or fiber rolls (not shown) or otherfiber sources. The fibers 17 are, of course, the nanofibers describedabove having a diameter ranging from about 4 Å to 1 nm, and a nanodenier of about 10⁻⁹.

The above described vortex air suction not only whirls the tail end ofthe yarn 19 to effect a twist it also draws new fibers 17 to besuccessively twisted into such a construction. As the yarn 19 is beingdrawn off in an axial direction 23 opposite to that of the helicallycreated current 25, the helically created current imparts further twistto the construction, in a manner which may be described as whipping theyarn 19 around in a wave-like configuration. Since only one end of theyarn 19 is being held, further twist can be imparted to the systemwithout being lost.

To demonstrate the efficacy of the present invention, a device wascreated including a Y-shaped glass tube 14 to form spinning zone 13. Airvortex suction was created by a variably controlled air pressure flowingacross orifice 15 to cause a vacuum or suction within spinning zone 13.Fibers 17 were electrostatically charged by source 18 and then weredirected from the fiber source to the spinning zone 13 by means of theair pressure suction. Various tests were made to study the effects ofair pressure, air velocity, yarn linear density, take-off speed form thefiber source, and apparent twist of the yarn 19.

In FIG. 1, a core filament 27 is used as a core for the thus producedyarn 19, to form what may be designated as a hybrid yarn containing thecore filament 27 and fibers 17 affixed thereto as described above.Examples of some textile fabric architecture that are suitable for thepresent invention are: biaxial woven, high modulus woven, multilayerwoven, triaxial woven, tubular braid, tubular braid laid in warp, flatbraid, flat braid laid in warp, weft knit, weft knit laid in weft, weftknit laid in warp, weft knit laid in weft laid in warp, square braid,square braid laid in warp, 3-dimensional braid, 3-dimensional braid laidin warp, warp knit, warp knit laid in warp, weft inserted warp knit,weft inserted warp knit laid in warp, fiber mat, stitchbonded laid inwarp, biaxial bonded, and xyz laid in system.

An Example of 3D braiding technology is an extension of the traditional2-dimensional braiding technology in which the fabric is constructed bythe intertwining or orthogonal interlacing of yarns to form an integralstructure through position displacement Fabricated in a circular orrectangular loom, shown in FIG. 2, a wide range of 3-dimensional shapesshown in FIG. 3 have been fabricated as part of the work herein. Theresulting linear fiber assembly or yarn is a hybrid of nano- and microfibers with a strong core filament, thus combining texture surfaces andstrength in one assembly. By properly controlling the processingconditions a wide variety of available surfaces, micro porosity andstrength can be tailored.

Depending on the tissue to be engineered, the linear fibrous assembliescan be fabricated into a wide variety of planar and 3-dimensionalfibrous assemblies by the textile manufacturing method. Depending on themanufacturing process, the resulting fiber architecture can be tailoredusing the porosity and tortuosity of these 3-dimensional fibrousstructures. They can be tailored by selecting different yarn sizes andyarn orientation. This technology can be illustrated with the3-dimensional braided structures shown herein. 3-dimensional braiding isattractive because of its versatility in designing microstructure andits capability of assuming net structural shapes.

The resulting linear fiber assembly or yarn will be a hybrid of nano-and micro fibers with a strong core filament, thus combining texturesurfaces and strength in one assembly. By properly controlling theprocessing conditions a wide variety of available surfaces, microporosity and strength can be tailored for tailored properties andperformance. Combination of nanofibrils with stronger fibers andfilaments Methods for converting nanofibrils into linear, planar, and3-D fibrous assemblies

One important embodiment of the present invention is the use ofnanofibers in medical implant surgery. It is well known that biologicaltissues consist of well organized hierarchical fibrous structuresrealign from nano to mm scale. The successful regeneration of biologicaltissue and organs calls for the development of fibrous structures withfiber architectures conducive to cell deposition and cell proliferation.Of particular interest in tissue engineering is the creation ofreproducible and biocompatible 3-dimensional scaffolds for cell ingrowthresulting in bio-matrix composites for various tissue repair andreplacement procedures. The present invention is admirable suited forthat technique.

Many of the aforementioned textile architectures are suitable for tissueengineering applications with nanofibrils. This requires a thoroughunderstanding of the structural geometry, including fiber tortuosity andfabric porosity as characterized by a fiber volume fraction-orientationanalysis.

To demonstrate the efficacy of this procedure, PLAGA bioabsorbablepolymer was placed in spherical, nanofibrils and aligned and3-dimensionally braided with 20 μm filaments seeded with osteoblastsover a two week period, resulting in complete success of the procedure.

While particular embodiments of the present invention have beenillustrated and described, it is not intended to limit the invention,except as defined by claims appended hereto.

What is claimed is:
 1. Apparatus for forming a textile structure,comprising: a source of fibers having a diameter ranging from about 4angstroms to 1 nm, and a nano denier of about 10−9; means forelectrostatically charging said fibers and transferring said chargedfibers; a vortex tube for forming an air vortex created helical currentformed by air suction at one end of said tube; inlet means drawing saidcharged fibers into said tube to cause said fibers in said air vortexcreated helical current into contact with one another to form a yarn;outlet means drawing said yarn from the other end of said air vortexhelical current tube; and fabrication means for receiving said yarn andforming said yarn into a textile structure.
 2. The apparatus of claim 1,wherein said textile structure is two dimensional.
 3. The apparatus ofclaim 1, wherein said textile structure is three dimensional.
 4. Theapparatus of claim 1, wherein said textile structure is formed into astructure having a 30 shape.
 5. The apparatus of claim 4, wherein saidstructure is fabricated using a circular loom.
 6. The apparatus of claim4, wherein said structure is fabricated using a rectangular loom.